1. Field of the Invention
The present invention relates to a method of assigning slots in an Ultra-Wide Coherent Optical Local star network and to an electronic device for carrying out the method.
2. Description of the Prior Art
As known, a UCOL network is a passive optical star network i.e. having stations connected to a star center via two-way dedicated optical waveguides.
One waveguide is used for transmission from the station to the star center and the other for receiving.
Each optical waveguide transmits optical signal over multiple channels. The particular optical waveguide allows several channels to be frequency division multiplexed and used for several transmissions on the same waveguide thus optimizing the link resources.
In a UCOL network, for each single channel, a transmission scheme based upon the use of a frame with a length of one millisecond, is adopted, its structure being described in an Italian patent application No. 21112 A/89 (filed Jul. 6, 1989) of the same applicant having a corresponding U.S. patent application No. 07/549,371.
In control data present in the frame, there is data which regulates the access of stations to the physical medium, i.e. those enabling each station to determine which of the data slots in the frame are reserved to the station itself for transmitting its own traffic.
It is important to point out that this type of information transmitted in a frame N is used for arbitrating the access of a following frame N+1 to the informative field.
Each station receives control information with a delay in comparison with time reference of the optical network star center. Having received control information, the station processes it to determine slots of a next frame which it will be allowed to use.
Successively, at the beginning of the following frame, the station may start to transmit in the slots reserved to it, but once again, in comparison with the star center time reference, it has to advance its transmission by an amount of time equal to the optical network star center time delay which corresponds to the propagation time of the signal along the outward waveguide.
If the duration of a frame is one millisecond, since it has been established that the maximum fibre length is 80 Km with a corresponding propagation delay of 400 microseconds, one can infer that the time interval available for processing requests for slots is only 200 microseconds. Hence it is evident that such time interval is very small.